Various arrangements for lighting systems are known which provide both conventional and emergency lighting. Such emergency lighting is intended to be activated when the conventional lighting is no longer operative because the direct mains supply to the conventional lighting is no longer available or malfunctions. Emergency lighting is typically powered by a battery or other energy storage device. Conventional lighting is controlled by an on/off switch by means of which a user (or control system) can control whether the lighting is illuminated or not. Generally, emergency lighting is intended to be automatically illuminated when the absence of mains power or the malfunction of mains power for the conventional lighting is detected in some way. Emergency lighting may be used to allow escape from buildings that would otherwise be in darkness due to the inoperativeness of the conventional lighting.
Emergency lighting and conventional lighting may share components. For example, the same lamp (such as a gas discharge lamp or light emitting diode) may be used for both conventional and emergency lighting. Other components may also be shared.
A lighting system comprising emergency lighting and conventional lighting may be considered to have two operating modes. In a normal mode, when the direct mains supply is operating normally (within the normal voltage range), a switched mains input, controlled by an on/off switch, is monitored, and the lamp is illuminated or extinguished in dependence upon the switched mains input. In an emergency mode, when the mains supply is not available or is malfunctioning (is outside the normal voltage range), the lamp is illuminated automatically, irrespective of the status of the switched mains input, using power from a battery or other storage element.
FIG. 1 shows schematically the elements of a lighting arrangement that provides both a normal mode and an emergency lighting mode. A mains AC supply 1 provides power in the normal mode to a mains ballast 3 optimized for use with the mains supply 1. The mains ballast 3 drives the lamp 5 when a mains relay 7 is closed. A control circuit (not shown) monitors the mains AC supply 1. If the control circuit detects that the mains AC supply is interrupted, or if it is determined to be malfunctioning (operating outside an acceptable range of values), the control circuit may provide an appropriate signal to relay control line 9 to open the mains relay 7 and to close an emergency relay 11. The emergency relay 11 allows the lamp 5 to be driven in an emergency mode.
To provide the emergency mode, the emergency lighting arrangement includes, in addition to the mains relay 7, relay control line 9 and emergency relay 11, a battery charger 13, a battery 15 and an emergency driver 17.
When the mains AC supply 1 is operating normally (and the lamp 5 is powered by the mains ballast 3), the battery 15 is charged (continuously or when required) by the battery charger 13. The battery charger 13 provides galvanic isolation between the AC mains supply 1 and the battery 15. When the control circuit detects that the AC supply 1 is interrupted (or malfunctioning), the emergency relay 11 is closed (the mains relay 7 is opened), and the emergency driver 17 illuminates the lamp 5 using power from the battery 15. Emergency driver 17 provides galvanic isolation of the battery 15 from the lamp 5.
As will be known to those skilled in the art, gas discharge lamps, such as fluorescent lamps, require an arc voltage to be applied between the lamp electrodes by a lamp arc supply. For most gas discharge lamps the lamp cathodes are heated by a cathode supply in order to heat the cathode filaments to cause them to emit electrodes into the gas within the lamp tube by thermionic emission.
Known emergency lighting arrangements do not provide an effective way of controlling lamp power for optimum lamp operation.
Known emergency lighting arrangements do not provide an effective way of controlling the battery discharge for optimum battery operation.